title: Effect of intense pulsed light treatment on human skin in vitro: analysis of immediate effects on dermal papillae and hair follicle stem cells.
abstract: BACKGROUND
  Hair follicles house a permanent pool of epithelial stem cells. Intense pulsed light (IPL) sources have been successfully used for hair removal, but long-term hair reduction may require several treatments. Many questions remain regarding the impact of IPL treatment on the structure of the hair follicle, more specifically on hair follicular stem cells and dermal papilla cells, a group of specialized cells that orchestrate hair growth.
  
  
  OBJECTIVE
  To characterize the destruction of human hair follicles and surrounding tissues following IPL treatment, with more attention paid to the bulge and the bulb regions.
  
  
  METHODS
  Human scalp specimens of Fitzpatrick skin phototype II were exposed ex vivo to IPL pulses and were then processed for histological analysis, immunodetection of stem cell-associated keratin 19, and revelation of the endogenous alkaline phosphatase activity expressed in dermal papilla cells.
  
  
  RESULTS
  Histological analysis confirmed that pigmented structures, such as the melanin-rich matrix cells of the bulb in anagen follicles and the hair shaft, are principally targeted by IPL treatment, while white hairs and epidermis remained unaffected. Damage caused by heat sometimes extended over the dermal papilla cells, while stem cells were mostly spared.
  
  
  CONCLUSIONS
  IPL epilation principally targets pigmented structures. Our results suggest that, under the tested conditions, collateral damage does not deplete stem cells. Damage at the dermal papilla was observed only with high-energy treatment modalities. Extrapolated to frequently treated hairs, these observations explain why some hairs grow back after a single IPL treatment.
authors.affiliation: Axe Médecine Régénératrice, Centre LOEX de l'Université Laval, Centre de Recherche du Centre Hospitalier Universitaire (CHU) de Québec, Québec, QC, Canada; Département de Chirurgie, Faculté de Médecine, Université Laval, Québec, QC, Canada.
authors.forename: D
authors.initials: D
authors.lastname: Larouche
authors.forename: D H
authors.initials: DH
authors.lastname: Kim
authors.forename: G
authors.initials: G
authors.lastname: Ratté
authors.forename: C
authors.initials: C
authors.lastname: Beaumont
authors.forename: L
authors.initials: L
authors.lastname: Germain
mesh_terms: D000368:Aged; D004847:Epithelial Cells / Q000528:radiation effects; D018859:Hair Follicle / Q000528:radiation effects*; D006204:Hair Removal / Q000379:methods; D006801:Humans; D008027:Light; D008875:Middle Aged; D010789:Phototherapy / Q000379:methods*; D012535:Scalp / Q000528:radiation effects; D012880:Skin Pigmentation / Q000528:radiation effects; D013234:Stem Cells / Q000528:radiation effects*